This invention relates to emission control systems for internal combustion engines, specifically to methods and apparatus for reducing emissions attributable to the imperfect seal that inherently exists between the pistons and cylinders of an internal combustion engine having reciprocating pistons.
Imperfect sealing inherently exists between the pistons and cylinders of reciprocating-piston internal combustion engines, such as those used in most automobiles. This imperfect sealing results in a certain portion of the combustion gases leaking past the pistons into the crankcase of the engine. Historically, these combustion gases were vented into the atmosphere to prevent build-up of excessive pressure in the crankcase and, especially in larger industrial and marine engines, to prevent the build-up of combustible gases in the crankcase, which could lead to a crankcase explosion. Venting of crankcase gases, however, resulted in a substantial quantity of unburned hydrocarbons being released into the atmosphere.
In the late 1950's positive crankcase ventilation (PCV) systems began to be incorporated into automobile engine systems as an alternative to atmospheric venting. PCV systems draw air through a breather into the crankcase where the air mixes with the combustion gases accumulating in the crankcase. This mixture is then drawn out of the crankcase into the intake manifold of the engine from whence it is then admitted to the combustion chamber and re-burned along with a fresh charge of air-fuel mixture. By circulating the combustion gases from the crankcase back into the combustion chamber, the escape of unburned hydrocarbons directly from the crankcase into the atmosphere is essentially eliminated.
Various methods have been devised for metering the flow of this mixture into the intake manifold for re-combustion. U.S. Pat. No. 3,445,285 to Sheppard discloses a metering valve that adjusts the flow rate in response to crankcase pressure while remaining relatively unaffected by intake manifold vacuum. U.S. Pat. No. 3,165,097 to Lowther discloses a metering valve responsive to intake manifold vacuum that operates between two relatively restrictive positions and a relatively non-restrictive position. All PCV systems rely on the admitting of fresh air into the crankcase to mix with combustion gases before the gases are re-burned.
It has also been recognized that combustion gases entering the crankcase are a primary source of contaminants that foul the engine lubricating oil. U.S. Pat. No. 4,760,833 to Tatyrek discloses that maintaining a partial vacuum in the crankcase reduces the rate at which the lubricating oil is contaminated by combustion gases.
No prior art appears to recognize, however, that the imperfect seal between the piston and cylinder, in addition to permitting the escape of combustion gases into the crankcase, permits a reverse flow of lubricating oil and other contaminants from the crankcase into the combustion chamber. This reverse flow of contaminants is believed to result in an increase in tailpipe emissions, especially carbon monoxide. The effect of this reverse flow of contaminants is exacerbated by the imperfect seal that also exists between the vane stems and vane guides of the engine, which also permit lubricating oil and other contaminants to-enter the combustion chamber.
Accordingly, a principal object of the present invention is to provide a method and apparatus for reducing both crankcase emissions and tailpipe emissions attributable to the imperfect sealing between the pistons and cylinders and between the valve stems and guides of internal combustion engines, by maintaining a substantially constant partial vacuum in the crankcase.
Another objective of the present invention is to reduce the rate at which engine oil is contaminated by combustion gases, without adversely affecting tailpipe or crankcase emissions.